Traditionally, pistons used in internal combustion engines (ICE) have been of a unitary construction. These pistons have been made from cast iron or steel. As fuel economy has become a more significant factor in ICE design, engine makers have had to develop lighter weight pistons capable of operating at higher temperatures for more efficient engines. These efforts have typically involved two different approaches; the use of lighter weight materials or the use of materials having higher melting temperatures.
The typical choice for a lighter weight material to replace cast iron or steel is aluminum. Aluminum has a lower density and is easily machinable. Aluminum also has high thermal conductivity and is corrosion resistant. Unfortunately, aluminum has lower yield strength than cast iron or steel at the normal operating temperatures of pistons.
The second approach to solving this problem typically involves the use of a material with a higher melting point. The operating temperature of an engine is increased by using higher melting point materials. The relationship between high operating temperatures and efficiency is well understood by those skilled in the art. Unfortunately, higher melting point materials are typically more expensive than cast iron or steel, or cannot be fabricated to solve the problem in a cost-efficient manner.
As a result, the two-piece piston assembly has been developed as a compromise. The two-piece assembly allows two different materials to be used in the construction of a piston. The design usually has a lighter weight, the side being composed of a lighter material with a heavier, more thermally stable, crown material. The two-piece piston assembly allows the vehicle manufacturer to obtain both advantages of the original solutions to this problem and optimize the performance of ICE's.
The present invention is particularly useful for conventional automobile ICE's but may also be used with diesel ICE's.
The present invention employs the concept of a two-piece piston assembly and introduces further refinements into the assembly. The invention teaches the proper selection of joining surfaces to couple the two pieces of the piston assembly to reduce weight. The invention also teaches a method of fastening the piston assembly to the piston rod to eliminate the external holes in the piston assembly.
The invention also teaches a piston that has a reduced "dead-air space." Dead-air space is the space between the annular top ring groove on a piston crown and the top of a piston. The reduction of dead-air space improves fuel efficiency, increases engine power, reduces emissions, and improves engine performance.